Artificial implant materials conventionally used for remedying breaks or voids made in bones or tooth roots by excision include the patient's own bones, similar bones provided by close relatives, other dissimilar bones, and metallic, organic and carbon materials. However, if a patient's own bone is to be used, the patient would suffer a severe pain in that a bone organization must be cut from a location other than the affected part. In addition, there may not always be sufficient bone available to provide an adequate amount of bone required for the remedy, so that it is often required to use a substitute to make up the shortage. In order to utilize similar or dissimilar bones other than a patient's own as a substitute, it is required to perform a surgical operation on an other living organism, which would impose a heavy burden on the bone donor.
On the other hand, metallic implant materials do not only lack affinity with living organism, but also have the disadvantage that metallic ions will plate out of the implant material into the human body, resulting in deterioration of the material. Such metallic ions may also be poisonous to man. For these reasons, metallic implant materials have proven unsuitable for permanent use. This is also true of organic and carbon materials.
In an attempt to overcome the aforesaid disadvantages, single-crystal or polycrystal alumina, silica, alumina or calcium phosphate-based glass, and ceramics such as apatite (see Japanese Patent Application Public Disclosure No. 52-64199, for example) have recently been proposed for use as implant materials. Composite materials comprising a metallic core flame spray coated with hydroxy-apatite powders are also known as disclosed in Japanese Patent Application Public Disclosure No. 52-82893. These ceramic materials are superior to other materials in that they have a high affinity with living organism and provide direct and intimate connection with bone organization. Especially, hydroxy-apatite is known to be a main inorganic ingredient of a bone or tooth. In this regard, calcined synthetic hydroxy-apatite draws an increasing attention as so-called artificial implant materials for artificial tooth, bone and the like since such apatite exhibits so good affinity with bone and tooth organizations as to bond directly and chemically with the bone organization and gums. (See, for example, The Chemistry and Industry, Vol. 37, No. 4, P.243, 1984.) Artificial tooth roots of calcined apatite and artificial bones of porous apatite have reached the stage of practical use.
However, calcined apatite is a brittle material which is vulnerable to tension, although highly resistant to compression, so that such apatite tends to have its tensile strength greatly reduced if a hair crack should be developed on the surface of the apatite due to a shock. This narrows down the width of application of calcined apatite to living organism. The use of such material has thus been limited only to artificial tooth roots for molar teeth or the like where no excessive tensile stress will be exerted. Moreover, when such material is to be used as fillers for breaks in bone, difficulties are involved in shaping the material in conformity with the intricate contour of the affected part.
In an attempt to eliminate the shortcomings of the calcined apatite described above, Japanese Patent Application Public Disclosures Nos. 57-117621 and 58-54023 disclose inorganic apatite fiber in which the apatite is made fibrous so as to suit the use as implant material for breaks or voids in bone. However, the apatite fiber as disclosed in these patent application public disclosures is fabricated by the so-called melt spinning process involving the steps of melting apatite at a high temperature and spinning it. As stated also in said disclosures, such melt spinning process requires that apatite be melted at a high temperature of 1500.degree. C. As a result, the apatite is deprived of its hydroxy group, and hence the `affinity`. The apatite fiber thus has a serious disadvantage in that it does not provide adequate compatibility with living organism in contrast to hydroxy-apatite. For this reason, such melt spun apatite fiber required a post-treatment for providing it with `affinity`.
If apatite is to be made fibrous without being deprived of the hydroxy group, the melt spinning process cannot be employed, but an other method such as the solution spinning process should be taken into consideration. However, since no binder or no spinning or calcining method suitable for use with the solution spinning process has been developed, it has heretofore been impossible to make apatite in fibrous form, particularly in cotton-like or fabric form with the hydroxy group retained as such.
After extensive researches and studies with a view to overcoming the prior art shortcomings as described above, the inventors of the present invention have discovered that it is possible to manufacture fibrous apatite, particularly cotton-like apatite and nonnwoven fabric thereof by solution spinning apatite with the use of special binder to make the apatite in fibrous form, particularly in cotton-like and nonwoven fabric form, and calcining the thus made apatite.
It is accordingly an object of this invention to provide apatite material in fibrous form, particularly in cotton-like and nonwoven fabric form having many applications such as uses for medical treatment, large scale microorganism cultivating media and others.
Another object of this invention is to provide hydroxy-apatite material in fibrous form, particularly in cotton-like and nonwoven fabric form which has excellent compatibility with living organism and superior physical properties such as tensile strength and the like.
Still another object of this invention is to provide a method of producing the apatite material of the type described in fibrous form, particularly in cotton-like and nonwoven fabric form.
Yet another object of this invention is to provide apatite implant material having a good compatibility with living organism and a high workability.